Tech Center: Brakes on Short tracks

NASCAR Sprint Cup Series race cars feature three pedals, and all are important

The most important pedal, for reasons that really need no
description, is the throttle. Without it, the car is a really slick
static advertising panel worth a couple hundred thousand dollars. The
clutch is important because it links up the 800-plus-horsepower engine
to the transmission and turns it from slick advert panel to moving
billboard.

The third pedal, while not as sexy as the other two, is absolutely essential: the brake pedal.

With Bristol Motor Speedway on the horizon, the brake pedal is going to be even more important than it already is. Richmond in a few weeks is the same way. Any short track is going to put a premium on braking, and even 1-mile tracks like New Hampshire are a brake tech’s worst nightmare.

Bristol is a place where beating and banging is an art form and the nose
of the car is for something besides holding the brake ducts in place.
The brake ducts at a short track are very important, because if there’s
no air, there’s too much heat, and if there’s too much heat, bad things
happen.

Modern brake packages are such an improvement over the
old-style systems. Four- and six-piston calipers, rotors engineered with
all the care of the space shuttle, brake fans and the whole nine yards
make it so.

Bristol is a rhythm track as much as anything. Hard
on the gas, off and onto the brakes hard, float through the center with
the car rotating beneath you and then hammer down off the corner. You do
it all again in about five seconds, so on and so forth.

Bristol is easier on brakes than Martinsville
because of the banking and the speed. Average speed at Bristol is in
the 120-mph range, while Martinsville is much slower. The banking also
slows the car a touch, because you’re transferring weight into the right
side of the car.

With the changes to the banking at Bristol,
it’s a little easier on brakes than it was in the past. If you got too
far into the corner and went up the track, you were either going to spin
out or you were going to get rooted off the bottom.

If you got
rooted off the bottom, it was like getting on an express elevator to the
back of the pack. With the progressive banking (minus the top part,
which was shaved off to make it more like the old track), you can run
the top groove.

That makes it easier on the brakes, because you
can drag them a little more to set the car and then float, prior to
putting the hammer down.

The G forces at Bristol are already
incredibly high due to the banks, and heavy braking makes it worse. At
Martinsville, for instance, drivers are at 3.6 Gs under straight-line
braking and under 2 Gs of force when standing on the loud pedal.

As
you know, the inside of a NASCAR stock car is very toasty. Depending on
the weather, it can reach 130 degrees inside the cockpit. When you’re
bundled up in the latest Nomex gear, it feels like the surface of the
sun.

The heat generated by the engine is one thing. There are
shields and such to deflect the heat away from components critical to
operation. The headers especially are nearly molten, and that heat has
to go somewhere.

With the heat shields in place, there’s still a
lot of ambient heat to deal with, and the teams use bead blowers to keep
them away from the tires. Tires are made out of rubber, and rubber,
like most other compounds, has a specific melting point.

This is
especially true at the bead of the tire. The bead is the part that tucks
up inside the rim and holds the tire on the wheel. It can melt easily,
and when you break the seal, the air (nitrogen, actually) goes where the
leak is. That means the tire loses pressure, the driver loses control
and the team usually loses all or part of a race car.

There’s a
handling aspect to keeping the heat of the brakes away from the bead as
well. The hotter the tires get, the more pressure builds inside the
tire. Under-inflated tires are bad in the sense that they tend to wear
the shoulders and roll over the sidewall. Over-inflation is a bad thing
too, because it means the wear is in the center of the tire and the
spring rate changes. That means the car plows, further wearing the tire
and eventually causing it to lose pressure…often explosively.

Staying
cool is important in a late-summer race like Bristol, and keeping the
brakes cool is even more important on a fast, tight track like Bristol.

NASCAR® and its marks are trademarks of the National Association for Stock Car Auto Racing, Inc. RaceView® and Streak to the Finish™ are trademarks owned by Turner Sports, Inc. and used under license. All other trademarks are the property of their respective owners.

NASCAR.com is part of Bleacher Report – Turner Sports Network, part of the Turner Sports and Entertainment Network.